Japanese Patent Disclosure No. 11-340517 discloses a semiconductor light emitting device which comprises an insulating substrate formed with wiring conductors, a semiconductor light emitting element attached on a main surface of the substrate, a reflector (a light reflecting plate) surrounding the semiconductor element on the substrate, and a light-transmissible plastic encapsulant for sealing the semiconductor element and reflector wherein the insulating substrate of the semiconductor light emitting device is mounted on a circuit board in the horizontal condition.
FIG. 12 illustrates a known semiconductor light emitting device or light emitting diode which comprises an insulating substrate 100, an island wiring conductor or die pad 120 and a terminal wiring conductor or bonding pad 130 formed separately from each other on a main surface 101 of insulating substrate 100, an semiconductor element or light emitting diode chip 140 secured on island wiring conductor 120, a lead wire 150 for electrically connecting an electrode on an upper surface of semiconductor element 140 and terminal wiring conductor 130, and a light-transmissible plastic encapsulant 160 for sealing each portion of island and terminal wiring conductors 120, 130 on main surface of insulating substrate 100, semiconductor element 140, and lead wire 150.
Island and terminal wiring conductors 120, 130 extend outwardly on main surface 101 of substrate 100, then are bent downwardly along each end surface 103, 104 and moreover are bent along a bottom surface 102 of substrate 100 to form bottom contact electrodes. Light emitted from an upper or side surface of diode chip 140 is irradiated to the outside through plastic encapsulant 160. The shown light emitting diode device can be surface-mounted in the horizontal condition on a circuit board (not shown) with bottom surface 102 of substrate 100 in contact to the circuit board.
This light emitting diode device comprises a reflector 110 on main surface 101 of substrate 100 for surrounding diode chip 140. Substrate 100 is formed of glass fiber into a plate of the rectangular section with flat main and bottom surfaces 101, 102, and the plate is impregnated with resin. Island and terminal wiring conductors 120, 130 are formed by plating nickel and gold in turn on copper base materials attached to substrate 100 according to a printing technique. Island wiring conductor 120 comprises an island 121 formed on main surface 101 of substrate 100, an island electrode 122 extending from one end of main surface 101 of substrate 100 through end surface 103 to one end of bottom surface 102, and a narrow island wiring 123 on main surface 101 of substrate 100 for electrically connecting island 121 and island electrode 122.
Terminal wiring conductor 130 comprises a terminal 131 on main surface 101 of substrate 100, a terminal electrode 132 extending from the other end of main surface 101 of substrate 100 through end surface 104 to the other end of bottom surface 102, and a terminal wiring 133 on main surface 101 of substrate 100 for electrically connecting terminal 131 and terminal electrode 132. Terminal 131 is disposed out of a central line 108 to reduce a longitudinal length of substrate 100 for manufacture of light emitting diode in smaller size with reflector 110 that has a ring portion 111 on main surface 101 of substrate 100.
Semiconductor light emitting element 140 is a gallium compound semiconductor such as gallium arsenic (GaAs), gallium phosphorus (GaP), gallium aluminum arsenic (GaAlAs), aluminum gallium indium phosphorus (AlGaInP), etc. A bottom electrode (not shown) formed on a bottom surface of light emitting element 140 is secured substantially on a central portion of island 121 through an electrically conductive bonding agent. An upper electrode (not shown) on an upper surface of light emitting element 140 is connected to terminal 131 through lead wire 150 striding over ring portion 111 of reflector 110.
Reflector 110 has a ring portion 111 and flange portions 112 provided on opposite outer sides of ring portion 111 and is formed of liquid crystal polymer or ABS resin blended with white powder. Formed inside of ring portion 111 of reflector 110 is a reflecting surface 113 which is upwardly diverged or flaring to form a portion of conical, spherical or paraboloidal surface or similar surface thereto or combined surfaces thereof. A bottom end of reflecting surface 113 is positioned within island 121 to dispose light emitting element 140 inside reflecting surface 113 of ring portion 111 which is higher than light emitting element 140. Ring portion 111 is formed on the outer periphery of island 121, inner end of island wiring 123 and inner end of terminal 131. Flange portions 112 of reflector 110 are formed along opposite sides 105, 106 of substrate 100 and extends inwardly or widthwise to merge with ring portions 111.
Plastic encapsulant 160 comprises a pair of ramp surfaces 161, 162 which are positioned respectively inside of wiring conductors 124, 134, and incline respectively relative to end surfaces 103, 104 at a given angle, a pair of vertical surfaces 163, 164 which are substantially flush respectively with side surfaces of substrate 100, and a flat top surface 165 between and substantially normal to vertical surfaces 163, 164. As seen in FIG. 12, plastic encapsulant 160 seals island 121, terminal 131, each inner portion of island and terminal wirings 123, 133, reflector 110, light emitting element 140 and lead wire 150, except wiring conductors 124, 134, and each outer portion of island and terminal wirings 123, 133. Each flange portion 112 of reflector 110 has a bare side surface 114 which is flush with side surface 105 or 106 and vertical surface 163 or 164 of plastic encapsulant 160. Island and terminal electrodes 122, 132 and each outer end of terminal wirings 123, 133 extend out of plastic encapsulant 160.
Recent attempts have been made to adopt such semiconductor light emitting devices as light sources for traffic signals or rear lumps of automobile, and in this case, semiconductor light emitting devices must produce the greater light output for a viewer to certainly and visually observe turning on or off of the light source from an off position. To this end, new high power light emitting semiconductors have already been developed to produce a high intensity light when relatively large electric current for example more than 350 mA (milliamperes) is supplied to the light emitting semiconductor element. However, when the element is activated with a large electric current over 350 mA, it may heat a surface of the element to a temperature above 150° C. Accordingly, prior art semiconductor light emitting device cannot produce a high light output because heat from the light emitting semiconductor element cannot efficiently be diffused or radiated.
Also, there is another attempt for adapting the semiconductor light emitting device of this kind to a backlight source for a liquid crystal panel or the like. Such an application of the device requires a vertical mounting structure of the device capable of directing light from light emitting element parallel to a mounting surface of a circuit board on which the device is attached. Simultaneously, the device is also required to selectively form a horizontal structure capable of directing light from light emitting element perpendicularly to the mounting surface of circuit board. Accordingly, two kind of prior art semiconductor light emitting devices had to separately be formed into vertical and horizontal mounting structures with different package configurations in response to vertical and horizontal mounting on circuit board. It is therefore desirable to develop a semiconductor light emitting device of a single configuration selectively applicable to vertical and horizontal mounting.
An object of the present invention is to provide a semiconductor light emitting device capable of efficiently diffusing heat from a semiconductor light emitting element to the outside through a support plate for bearing the light emitting element when heavy current flows therethrough for stronger lighting. Another object of the present invention is to provide a semiconductor light emitting device of a single configuration selectively applicable to vertical and horizontal mounting. Still another object of the present invention is to provide a semiconductor light emitting device which can improve light directivity and axial brightness or luminance. A further object of the present invention is to provide a semiconductor light emitting device which may be manufactured by preferably injecting and filling resin within interior of reflector in forming a plastic encapsulant.